The UN’s deputy secretary general has accused President Donald Trump of “treading water” over a decision on the future of the Paris climate change agreement, on which the fate of millions of people depend.

Amina Mohammed told the Guardian she was hopeful the US would not renege on the deal signed last year, but that Trump appeared to be avoiding a public declaration after taking such a hard line during his campaign for the White House.

Trump has previously described climate change as a hoax orchestrated by China. During his battle for the presidency against Hillary Clinton he vowed to “cancel” the historic agreement, which commits countries to ensuring that the average global temperature does not rise 2C above pre-industrial levels.

Since being elected Trump, who is on a world tour starting with a visit to Saudi Arabia, has delayed announcing his administration’s position, although it is widely believed he will be forced to make a statement at the G7 summit in Italy next weekend.

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Mohammed said: “[The US] coming out of the agreement does put the track for the ambition of attaining the target in jeopardy and we have to claw that back and make sure that doesn’t happen.”

Under the Paris agreement’s “members determined contributions” (MDCs), former president Barack Obama pledged to cut US carbon dioxide emissions by 26% by 2025, bringing it down to 28%.

Mohammed, a former environment minister in the Nigerian government, said the White House, while generally sceptical of the detailed terms of the agreement, appeared divided over what steps to take.

She said: “As far as the US administration’s discussions are concerned, on the one hand there is the case of staying in the agreement and determining how they would respond to the MDCs and the commitments of the previous administration. They would rather be at the table than not.

“On the other hand, there is the other side that says even if you stay in the agreement there is no room for manoeuvre. Those two positions are being worked out. We continue to talk to both sides about the imperative to stay and give the opportunity to go through the MDCs and work together with them on that.

“I think he is treading water until he has to say something, probably at the G7 meeting. Maybe he will find a reason why he is not ready then either. What we have seen is there is an understanding in his administration that withdrawing from the agreement is not the best and they would probably be better served to stay in.”

Obama hailed last year’s Paris agreement as a historic “turning point” in the fight against climate change, should countries fully commit to cutting emissions.

Mohammed said the president needed to be persuaded that while jobs might be lost in the coal industry, they would be regained in renewables if the US stuck to its promises.

She said: “The world has recognised that climate change is very real, the science shows emissions are having a detrimental effect and will be catastrophic unless we try to reduce them below two degrees and certainly 1.5. And so, the US being one of top emitters it is essential to have them in the agreement.

“Globally, the implications are huge for countries that will go under water, coastlines that will lose investment to high-level sea rises. This is very real. I see hope for the US staying in the agreement. I think there is a bigger challenge of us keeping the ambition of the MDCs.”